Grinding apparatus



Oct. 7, 1958 w, oc w ETAL 2,854,795

GRINDING APPARATUS 2 Sheets-Sheet 1 Filed Oct. 11, 1954 llla lrl iINVENTORS ATTORNEYS Oct. 7, 1958 W. E. MccowN ETAL 2,854,795

GRINDING APPARATUS 2Sheets-Sheet 2 Filed Oct. 11, 1954 (It Q96 A TTORNEYS finitedsates ara-11m GRINDING APPARATUS Application October 11, 1954,Serial No. 461,456 9 Claims. (Cl. 551-59) The present invention relatesbroadly to grinding, and more particularly to an improved method andapparatus for grinding surfaces by high frequency vibration.

Although the invention is not restricted to the grinding of anyparticular article or type of surface, it is especially well adapted tocarry out the difiicult job of grinding the surfaces of flat glasssheets and will be described in that connection here. i I

In the regular commercial productionof plate glass, the unfinished glassblanks are ordinarily bedded upon surfacing tables in a layer of plasterof Paris or the like and then passed beneath horizontal grinding discswhich are revolved in the presence of sand and water toobtain'thedesired grinding efiect. Because of the pressureof the grinding discsupon the sheets of glass in the conventional processes, the sheets aresubjected to a crushinglaction as the discs force the abrasive particlesinto the surface being ground. Consequently, the sheets oftentimesexhibit small cracks or fissures which affect the optical qualitiesthereof, and if numerous enough, cause the sheets to crack. 'Of course,any cracking of the sheets'not only has an adverse effect uponproduction efliciency, but also upon the felt-covered polishing discsused in subsequentpolishingsteps which are easily torn by sharp glassedges and chips.

' Further deficiencies are also grinding processes'in that it plic'atedprecision equipment be used to maintain the grinding discsin an exacthorizontal position with respectto the sheets passing therebeneath sothat a'uniformly ground surface may be obtained. Also, the large amountsof wat'er anddifierent grades of sand that are necessary to obtain thedesired grinding effect cause the grinding area to be damp, dangerous andunsightly thereby incr'easing maintenance and accident prevention costs.'According to the presentinvention, to alleviate the inherent incommercial so that the generating is necessary that heavycomabove-mentioned deficiencies that have been inherent in conventionalgrinding methods, vibration frequencies preferably over-100 cycles persecond'are applied to the surfaces of the sheets through a suitablemedium having an abrasive or grinding compound therein. These vibrationfrequencies are transmitted in the form of mechanical vibration soundwaves, and as the sound waves are propagatedthrough the mediurn, whichis preferably a fluid, the motion of the abrasive particles in saidmedium is related to the characteristics of the soundwaves themselves.{In'this manner, the sound waves create a cavitationlelfect iin theliquid medium; cavitation being the effect of Lthegal'ternate' formationand collapse of gas bubbles and cavities. This collapse of the cavitiescreates an a ation etfec tfof sufiicient magnitude to cause the abras veparticles'lto alternately bombard the surface of the sheets and torerodeor grind the said surface as the sheets are movedpastifthe. cavitationarea. k Ilius itlisitherefore a primary object of this invention toprovide airelatively simple and light weight device which will grindflat-surfaced bodies in an expeditious 2,854,795 PatetttedOct. 7, 1 9582 and efiicient manner by the use of sonic or ultrasonic vibrations.

Another object of the invention is to provide a means whereby aplurality of vibration generating elements may be mounted above the pathof a conveying means faces thereof will completely traverse the path ofthe articles carriedby the conveying means as they pass beneath saidgenerating elements.

Another object of the invention is to provide a means whereby a thinfilm of a liquid transmitting medium having an abrasive or grindingmaterial therein may be confined to a very small and localized area overthe surface being ground. i

A further object of the invention is to provide a method of grindingsheet material wherein relatively few grades of grinding orabrasivematerial are needed to produce a relatively smooth surface,

A still further object of the invention is to provide a method andapparatus for grinding glass sheets which will leave relatively fewfissures or cracks in said sheets.

Other objects and advantages of the invention will become more apparentduring the course of the following description when taken in connectionwith the accompanying drawings.

In the drawings wherein like numerals are employed to designate likeparts throughout the same:

Fig. 1 is a fragmentary plan view of one form of grinding apparatusconstructed in accordance with the invention; I

Fig. 2 is a transverse vertical section through a glass finishing lineshowing the apparatus of the invention mounted thereabove; g

Fig. 3 is aperspective view of one form of vibration generating elementthat may be used with the invention;..

Fig. 4 is a sectional view taken substantially along line 4- 4 of Fig.3; i

Fig. 5 is a partial vertical sectional view: taken along line 55 of Fig.1;" V v i 5 Fig. 6 is a partial side elevation of a means for themounting of the vibration generating elements} and ig. 7 is a sectionalview taken substantially along line77ofFig.6.

With reference now to the drawings and particularly to Figs. land 2,there is shown'one section ofafcontmuous grinding and polishinglineinade up of a series or conveying means '110 which are then passed13. As shown in vibration generating elements are identicalreciprocating supporting 14 and 15 arranged above the tables upon erallyat 20 (Figs. 1 and 6) formed between guide blocks 21 suitably secured tothe standards 16. l v

Movement of the respective cross beams 14 and 15 relative to one anotheris accomplished by'means' of'similar drive mechanisms 22. Specifically,the drive mechanisms 22 include a drive shaft 23 having'a bevel gear 24thereon and journaled in a bearing 25. Extending in a substantiallyvertical direction and suitably journaled by a bearing 26 in the upperplate 27 of support frame 28 is a shaft 29. Connected to the lower endof shaft 29 is a bevel gear 30 which engages and is driven by the bevelgear 24-011 drive shaft .23. On the upper end of shaft 29 there ismounted an eccentric or crank 31 whichhas a drive arm 32 pivotallyconnected thereto. As shown in Fig. 6, the said drive arm 32 is in turnpivotally connected to one of the slide plates 18 by means of a pin 33which fits in a suitable hole 34 in the said slide plate. Thus, for apurpose to be described hereinbelow, upon rotation of the drive shaft23, the shaft 29 and the crank 31 will be rotated causing the drive arm32 to reciprocate the respective cross beam connected thereto in theways 20. In other words, each of the cross beams 14 and 15 are connectedto similar individual drive mechanisms 22 which may reciprocate the saidcross beams together or in a staggered or opposed relationship withrespect to one another.

Provided on each end of the cross beams 14 and 15 adjacent the legs 17thereof are vertical flange portions 35 and horizontal flange portions36 which define rectangular openings 37 therebetween at the end of thebeam. Slidably mounted for vertical movement in each of the openings 37is an open frame-type clamping bracket 38. Mounted within the clampingbrackets 38 and bridging the tables are especially formed channels 39and 40 having grooves 41 therein; the channel 39 is secured to one sideof each of the brackets 38 by means of screws 42, and the channel 40 isslidably mounted along a finished slot 43 formed along anopposite sideofthe brackts 38, being held therein by an adjustment screw 44.

The transducers 13, which are preferably of a magnetostrictive typehaving laminated core 45 and electrical coil windings 46 (Figs. 3 and4), are supported by the channels 39 and 40 along nodal tabs 47 on thecore 45 which tabs fit into the grooves 4I of the channels 39 and 40.The nodaltabs 47 are located at a point of substantially zero vibrationof the transducer vibratory system so that a minimum of vibration energywill be imparted to the supporting structure thus allowing a maximumamount of energy to be expended upon the surface being ground. Securedto the vibrating ends of each of the transducer cores 45 by suitablescrews 48 are upper and lower protective shoes or plates 49 and 50respectively. In this connection, the lower shoe 50 serves as theworking face of the transducer and prevents the abrasive grindingmaterial from eroding the transducer core 45 and, in the event that thesaid shoe 50 should become unduly worn or eroded, it may be replaced'bysimply removing the screws 48. i

When'all of the transducers 13 are properly supported along the channels39 and 40, the whole bank of transducers may be vertically adjusted toplace the transducer working surfaces or faces 50 at the desired heightabove the surface to be ground by means of opposed adjustment screws 51(Fig. 6), held in place by lock nuts 52 and carried by the horizontalflange portions 36 of the cross beams 14 and 15. These adjustment screwsengage the clamping brackets 38 and provide a means whereby the bracketsmay be raised or lowered in the opening 37 defined by the flanges 35 and36, and thus cause the channels 39 and 40 to raise or lower thetransducers 13 to place them in proper position with respect to'thesurfaceof the sheets S carried by tables 10. The clamping brack' ets 38are kept in aligned position with respect to the vertical flanges 35 bymeansof keys .53 mounted on the inside of the flange portions whichengage key ways 54 formed in the sides of' the clamping brackets. Thus,when the brackets are moved upwardly and downwardly, the keys 53 engagethe ways 54'and allow the brackets and channels 39 and 40 associatedtherewith to move only in a vertical direction. Y

In accordance with the invention, as noted hereinbefore, a supply ofliquid energy transmitting medium having an abrasive or grindingmaterial thereinis maintained between the working surfaces 50 of thetransducers and the surface being ground so that a cavitation elfect canbe set up in the liquid medium which will cause the abrasive particlestherein to bombard and erode or grind the surface of the sheets. Thisenergy transmitting medium may be supplied between the working surfaces50 of the transducers and the sheets S through a tube 55 (Fig. 4)passing through the central portion of the transducers 13. Moreparticularly, the tube 55 is preferably formed of a pliable fiber orrubber material and is held in place in openings 56 formed in thetransducer core 46 by suitably threaded plugs 57. The plugs 57 have anopening 58 therein which mates with a flared opening 59 provided in theprotective shoes 49 and 50.

The energy transmitting medium may be brought to each of the transducers14 by means of rubber hose conduits 60, the lower ends of which fitsnugly in the upper plug 57 in the transducer core, while the upper endsmay be connected by a suitable joint 61 -to individual pipe sections 62positioned above each of the said transducers. In turn, each ofthe pipesections 62 are connected to a main distribution pipe 63 extending alongthe length of each of the support beams 14 and 15. Because of theflexible hose connections 60 and the flexible tubes 55 within thetransducers, the transducers may vibrate freely without having anydamping, efiects exerted thereon by the said conduits or tubes and thusmay impart a maximum amount of energy to the abrasive containing medium.

It will be apparent that as the abrasive containing liquid flows throughthe tube 55 in the transducer core under pressure, it will pass to theflared opening 59 in the lower protective shoe 50 and spread out ontothe surface of the sheet 5 as it leaves the said opening. In thismanner, it is possible to set up and maintain a film of fluid over anarrow area of the surface being ground. While thisfilm or layer ofenergy conducting liquid is extremely thin and vertically unconfined, itnevertheless completely fills the space between the transducer workingfaces 50 and the sheet surface due at least to some extent, to surfacetension and capillary attraction effects. These effects act to maintainthe energy conducting medium beneath the transducer faces at a levelsubstantially higher than that of the unconfinedfilm ofthe liquid thatflows away from the transducers onto the remaining portion of the sheet.on the other hand, for some applications, it may be desira le to placeth t n d cer working faces 50 in slight pressure contact with the sheetsso, that better vibratory contact may be had with the abrasiveparticles. If this were done, the thin film of the abrasive containingliquid may still be forced between the said working faces and the sheetsbeing ground in the same manner as described above. In any case,however, it will be evident that the liquid medium, although unconfinedmay be maintained in a thin but elfective layer over the necessarynarrow width'of surface being ground by the means described above, thuseliminating the need for tanks or other confining means to contain theliquid in sufficient volume to cover the transducer generating faces. 7

In order to obtain best results, the distance between the transducerworking faces 50 and the surface being ground can be varied by means ofthe adjustment described hereinbefore, and the distance providedtherebetween related to the surface tension and capillary attractioncharacteristics of the energy transmitting liquid being used.- Forexample, with liquids having the greater surface tension and capillaryattraction characteristics, the transducers can be maintained at agreater distance from the surface being ground inasmuch as the surfacetension will not be overcome as easily to permit the liquid to becomeseparated from the working'faces'50.

With the transducer position so determined, the conducting medium isdeposited therebeneath upon and over a narrow width of .the surfacebeinggroundwhere .it will substantially fill the narrowspace between thetransducer generating faces 50 andthe said surfaces and be maintainedtherebetween by the natural forces mentioned above. The transducers arethenenergizedby an alternating voltage supplied to the coils 46 thereofcausing extremely rapid vibrations to occur along the area .of theworking faces 50. Since the generating surfaces 50 are in directcontactwith the liquid medium, alternate positive and negative pressurefronts which travel directly from the vibrating surfaces or faces to thesurface being ground along a path normal thereto are created. Thesevariable pressure fronts cause a cavitation or bubble effect to takeplace in the medium which in turn causes the abrasive particles to bealternately accelerated toward the surface and pulled away therefromtoward the vibration generating elements as the bubbles collapse andcreate a negative pressure area. In this manner, bynthe highacceleration of the abrasive particles toward the surface,- the saidsurface is subjected to agrinding and smoothing effect asthe sheetsmoverelative to the. generating-faces 50 I 5 To aid in evenly distributingthe grinding action of the abrasive particles over the entire surface ofthe sheets as they are moved past the transducers by the tables 10, therespective support beams 14 and 15 are reciprocated at a relatively highrate of speed relative to one another by the drive mechanisms 21 so thatthe surfaces of the sheets are swept by the eroding action of saidparticles. In other words, the transducers are moved transversely of thepath of the sheets passing therebeneath so that a uniform grindingpattern will be obtained over the entire surface area of the sheets.

While for purposes of illustration, only two banks of transducers havebeen shown mounted above the path of the tables 10, it will be apparentthat any number may be used along with various grades of abrasives toobtain the desired grinding and smoothing effect. Some of the abrasivesthat may be employed include sand, boron oxide, aluminum oxide, rougeand others, which may be used alone or in combination to produce thedesired grinding effect. However, regardless of the type of abrasiveused, it will be evident that the sheets may be ground by the apparatusof the invention without the crushing .efiect that is ordinarilyinvolved with the large metal discs used in conventional processes,which as noted above, have a tendency to produce large numbers of cracksand fissures in the glass sheets.

While an energy transmitting medium of water may be advantageously usedin many cases, in others it is desirable to use a detergent medium asthe transmitting medium so that dirt and other undesirable particles maybe removed during the grinding operation. Alternately, other methods ofdisturbing the molecular structure of the surface being ground usingsimilar type vibration generating elements may be practiced. Forexample, if the sheets are susceptible to chemical reactions, an acid orother type medium may be used in conjunction with an abrasive to removeand grind the sheet surfaces.

Also, while the vibration generators used to produce the cavitationefiect in a liquid medium may operate continuously without interruption,it has been found that they overheat and tend to lose their efficiencywhen operated continuously for long periods of time. To compensate forthis condition, there is herein provided a cooling means which includesa pipe 64 mounted along the beams 14 and 15 above the transducers 13.The pipe 64 is provided with spray holes 65 which act to direct water orother suitable cooling mediums upon the transducers so as to provide acooling effect therefor and thus allow the transducers to operate atpeak elficiency. However, it is to be pointed out that other types ofcooling means may be employed such as cooling pipes which cool by heatabsorption, or air jets, etc.

Should it be desired to move any one of the transducersfromthesupportingbeams [14 and 15, they maybe removed therefrom by mereloosening of the adjustmentscrews44 so as to allow .the channels 4ersslide in the slot 43 thus causing them to disengage the nodal tabs 47.After the channel 40 has been withdrawn from contact with the transducertabs 47, any one of the transducers may be removed by'pulling the rubberhose 60 from contact with its associated plug 57 and by disengaging thetransducer power lead 66- and plug 67 from the power supply, housing68mounted upon the upper side of the supporting cross beams. V v 1 It:will alsobeapparent that while the grinding apparatus disclosed hereinhas been described in connection with the grindingof glass sheets, thatit may also be used to grind sheet material such as steel plate orplastic,

and that the transducers maybe moved while the object being groundremains substantially, stationary or moves relative thereto. Also, whilethe abrasive. medium has been shown in the drawings to be deposited uponthe sheets through a conduit passing through the transducers, it

may also be deposited upon thesheets by suitable external pipes whichmayspray thesaid medium between the working faces of the transducers andthe surface of the sheets.

It is of course to be understood that the form of the inventiondisclosed herein is to be taken as the preferred embodiment thereof andthat various changes in the shape, size and arrangement of parts may beresorted to without departing from the spirit of the invention or thescope of the following claims.

We claim:

1. Apparatus for grinding flat surfaced objects, comprising means formoving the objects to be ground along a definite path, a support mountedabove the path of said moving objects, a plurality of elastic vibrationgenerating elements mounted on said support in spaced relation to saidobjects, means for building up a layer of an abrasive containing energytransmitting medium on a localized area of said objects as they movepast said vibration generating elements, and means for reciprocatingsaid vibration generating elements laterally relative to said movingobjects during grinding of the latter.

2. Apparatus for grinding surfaces of objects as described in claim 1,in which means are provided for supplying said abrasive containingmedium through said vibration generating elements.

3. Apparatus for grinding glass sheets, comprising means for moving asheet to be ground along a definite path, a support mounted above saidpath, a plurality of vibratory devices for inducing elastic vibrationsmounted on said support in spaced relation to the glass sheet, means fordepositing an energy transmitting medium containing abrasive thereinbetween said vibratory device and said sheet, and means for moving saidvibratory devices substantially transversely of the path of said sheetduring grinding of the latter.

4. In a method of grinding a flat surface, the steps of moving saidsurface in face-to-face relation along a path past an elastic vibrationgenerating element, providing a film of an abrasive containing energyconducting medium between said surface and said vibration generatingelements and in contact therewith, and transmitting undamped elasticvibrations to said energy conducting medium from said vibrationgenerating element while moving said element in a plane parallel to saidsurface.

5. In a method of grinding a flat surface as defined in claim 4, theadditional step of moving said surface and said vibration generatingelement relative to one another during grinding of said surface.

6. In a method of continuously grinding a flat surfaced object as itmoves along a definite path, the steps of arranging a plurality ofvibration generating elements with their working surfaces in spacedrelation with the object to be around providing a film of an abrasivecontaining energy conducting medium between said object and said 7vibration generating elements, transmitting elastic vibrations' to saidenergy conducting medium from-said vibra sea generating :ele nents, fand moving someof said vibratibn'g'en'erating elements relative to oneanother in a planepar'allel to the flat surfaced object andduringgrinding thereof;

7. Apparatus for grinding glass surfaces,- comprising means for movinga" glass :s he'e t having a surface to-be ground along a definite path,support means extending across said path, elastic vibration inducingmeans mounted on said support means and having a working face positionedadjacent the path dftravel of the surface of said sheet, means forsupplying an abrasi've containing energy transmitting medium tothe'sheet surface to' be ground, and means for movingks'aid workingface-transve'rsely to the direction of movement of the glass sheetduring grinding of said sheet.

'8. Apparatus for grinding glass surfaces as defined in claim 7, whereinthe means ground during grinding of said sheet surface.

9. A method of surfacing glasssheets which comprise positioning a glasssheet with the surface to be treated for moving the working faceincludesmeans forrecip'rocatin'gthe support means in a parallel with the workingsurfaces of a plurality of vibration generating elements, conveying saidsheet surface past, said vibration generating elements along apredeterminedpathspaced from'but substantially parallel withsaidparallel working faces, maintaining an unconfined mass ofasuspens'ion of abrasive particles in an energy conducting li'q'iiidinthe space between the parallel working' faces of said vibrationgeneration elements and the portion ofsaid sheet surface that is movingtherepast and in contact with both, and transmitting elastic vibrationsto said unconfined mass of liquid.

ReferencesCited in the file of this patent UN'1 1ED STATES PATENTSUNITED STATES PATENT OFFICE CERTIFICATE OF CORECTIN PetenrNo, 2354 795@m '7 58 William EC. McGown It is hereby certified that error appears inthe printed specification of "the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

T w a Column 0 74, for "around" ea ground e Siged. and sealed this 27thof J 1959 (I SEAL) Attest:

ll AILLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents

